Damper windings for synchronous converters



Jan. 26, 1932. L. DREYFUS 1,842,583

DAMPER WINDINGS FOR SYNCHRONOUS CONVERTERS Filed Jan. 9, 1929 r /6 fl/jy, 20 /8 7 F915 3 F294 6 5 51* 1 1 1 1 I I ll! 5 4 2 4 l i r a 42 4 x 5 fm/e/fior Ludwig Drg MS Patented Jan. 26, 1932 v UNITED STATES PATENT OFFICE LUDWIG DREYFUS, OF VASTERAS, SWEDEN, ASSIGNOR TO ALLMANNA SVENSKA ELEK- TRISKA AKT'IEBOLAGET, OF VASTERAS, SWEDEN, A CORPORATION OF SWEDEN DAMPER WINDINGS FOR SYNCHRONOUS CONVERTERS Application filed January 9, 1929, Serial No. 331,253, and in Sweden August 25, 1927.

It is well known that a sudden increase of load, for instance a short-circuit, on the direct current side of a synchronous converter of the construction hitherto known causes a 5 iunting motionwhich has an unfavourable influence on the commutation, and in order to reduce this hunting the converter has generally been provided with a short-circuited damper winding.

I have now found that the direct influence of such a'damper winding arranged in the hitherto usual manner on the commutation has been insignificant if not even unfavourable but that, on the other hand, it is possible to arrange the damper winding in such a manner as to improve the commutation on such occasions. Such an arrangement of the damper winding is the object of the present invention.

The invention will be described with reference to the accompanying drawings in which Fig. 1 shows diagrammatically a synchronous converter having a substantially normal damper winding arranged around a commutating pole; Fig. 2 is a similar View but showing one form of this invention; and

Figs. 3 to 10 are diagrammatic Views showing different forms of the damper winding according to the invention.

In all the figures, 1 designates the cores of the main poles and 2 the cores of the commutating poles while 3 designates the damper bars arranged in the former cores; and in Figs. 1 and 2, 17 designates the armature core, 18 the armature winding, 19 the commutator, and 20 the sliprings. The end connections of the damper bars are arranged in different manners according to the invention for accomplishing the desired result.

: WVhen considering the influence on the commutation of the damper winding on the occasion of a short-circuit or other over-load suflicient to cause a release on the direct current side, attention has to be paid to the conditions during two difierent time intervals, namely, before and after the said release. During the first of these intervals the'current rises in the'direct current circuit at a rate which initially depends only on the self-induction in the said circuit; Simultaneouslv the current rises in the alternating current circuit and a current arises in the damper winding. The alternating current need not be considered if a portion of the direct current fully equivalent thereto is also neglected and only the rest thereof taken into account. Referring to Figure 1 which shows a substantially normal damper winding 3, 1, 5, if the zone between the main poles 1 is considered, it is found, that the resulting flux here should be zero as it is embraced by an entirely short-circuited winding. The M. M. F.s within this zone are derived from three sources, namely from the armature, from the commutating winding, and from the damper winding. The two first named ones are entirely defined by the external direct.

current, and the third one must then assume such a value that the aforesaid condition is satisfied.

If a commutating flux of any importance shall arise beneath the commutating pole 2, the flux between the latter and the main pole must not only be oppositely directed but also have suflicient space to develop. The innermost short-circuited turn of the damper wind ing must therefore not lie too close to the commutating pole, because in such case the commutating flux would be damped to Zero value which also would imply that the said innermost turn of the damper winding would carry a current of opposite direction to the other ones. A simple damper winding according to Figure 1 has therefore the most favourable influence if its axial damper bars lie exclusively in or near the main poles.

If on the other hand, as shown in Figure 2, there is inserted in series with the end connections 4, 5 of the damper winding an additional turn 6 around the commutating pole 2, the conditions will be entirely different. This turn is caused to carry the whole resultant of the currents in the individual bars 3,

the M. M. F. of which obviously must be opposits to that of the armature current and thus cooperate with that of the commutating winding. The condition that the resultant flux in the innermost short-circuited turn must be zero is of course still valid, but the reduction of the current in the damper bar in the edge of the main pole which is caused hereby has no appreciable influence on the total current which acts directly on the commutating pole.

The arrangement shown in Figure 2 can be modified in different manners. In Figure 8 an additional turn electrically equivalent to the loop 6 is produced around the comniutating pole 2 by dividing the end connections 4 into two different portions each having a cross bar 7 which forms the return path for the bars 3 but lies on the opposite side of the commutating pole with respect to these bars. The commutating pole is thus surrounded by as many ampere turns as in Figure 2. The difl'erence-from the last mentioned Figure lies in the fact that each main pole with its damper winding forms an independent iconstructional unit which can be replaced without loosening any soldered joints in the damper winding.

In certain cases it may nappen that the arrangement shown in F igure 2 r 3 causes a too strong commutating flux (over-commutation). This inconvenience may easily be overcome, for instance by introducing bars'S, Figure 4, which connect the end connections between the main and commutating poles and thus relieve the latter ones of certain ampere turns. By an appropriate placing of the bars 8 in the pole interval any intermediate action between that of Figure 1 and that of Figure 3 can be obtained For the same purpose the additional magnetizing loop 6 may embrace only a portion of the commutating pole, as shown in Figure 5, or particular short-circuits 9, Figure 6, electrically separated from the damper winding proper nu be placed between the main and cornmutating poles. The action of these circuits will be essentially analogous to that of the damper bars 8 in Figure 4. v The modifications shown in Figures 4-6 may of course be applied to the arrangement according to Figure 2 as well as to that according to Figure 3.

One or more additional turns carrying'the damper current and surrounding the commutating poles may also be produced in such manner that the damper winding is connected to the ordinary commutating windin 11 at suitable points 1.0, Figure 7. In this case however the portions of thedamper winding belonging to diilerent commutating poles must have no other mutual connection than that through the commutating poles, and therefore the end connections 5 of the damper winding must be interrupted in the middle of the main poles. With reference the main purpose of the damper winding these interruptions are of no essential importance.

The different damper bars 3 under the same main pole half may also be series-connected according to Figure 8 instead of parallelconnected as hitherto usual, and in series with the said bars acertain number of turns 12 on return to said position it will oscillate.

the commutating pole may then be connected. These bars may then in analogy with Figure 7 form a portion of the ordinary commutating winding.

During the second of the initially mentioned intervals, namely, after the interruption of the direct current, the converter in most respects behaves as a synchronous motor carrying no load. As known, it is generally strongly retarded as long as the short-circuit or the overload lasts, and in consequence it is considerably displaced from the noload position at the instant of cut-out, and during the If it could be regarded as a synchronous motor in all respects, these oscillations, which are gradually damped out, would cause no in-' c'onvemence,but for the proper working of the commutator they involve a serious danger, in that the damper currents which serve to retard the oscillations produce, since the direct current no longer exists, a flux in the commutating zone which may create a too high commutator bar voltage and thus cause a flash-over.

During this interval the damper currents are alternating currents of rather low frequency equal to the frequency of the mechanical oscillations and for this reason the ohmic resistance of the damper winding is of great importance for the current distribution, contrary to the interval before the release. It may therefore be necessary to increase the average resistance of the damper winding considerably above that hitherto generally regarded as appropriate for damping purposes, whereby the current in the external alternating currentv circuit (primary current) during the oscillation is reduced. In the pole interval containing the commutating zone, where the reluctance is high, the said primary current essentially determines the magnitude of the resulting flux, while the total value of the transverse flux is determined by external conditions (amplitude of the oscillation and reactance of the alternating current circuit). If thus the flux in the commutating zone shall be reduced, the primary current must be reduced by an increase of the ohmic. resistance of the damper winding. While this resistance has hitherto been 'kept lowerthan that corresponding to a maximum damping action, it is according to the present invention made higher than that giving the said maximum.

The leakage between the alternating current winding and the damper winding is in the pole interval generally so low on account of the high reluctance that the ohmic resistance in the innermost turn of the damper winding bars) will determine the resultant flux in the pole interval in a higher degree than the reactance. In order further to reduce this flux the resistance in the said innermost turn may (for parallel-connected damper therefore be made as small as possible at a high average resistance of the damper winding, namely, by making the portions 4 of the end connections lying in the pole interval with a low resistance, while all other portions of the end connections 5 and the axial damper bars have a high resistance, as has been indicated in Figures 1 to 7 by drawing the portions 4 in heavy lines.

In certain cases the steps now described for preventing a flash-over after disconnecting the load may be not sufficient and then the arrangement diagrammatically shown in Figure 9 or in Figure 10 be used instead of those described. In Figure 9, where the damper winding proper is arranged in analogy with Figure 8, the portion 12 of the said winding immediately surrounding the commutating pole is connected at its terminals to a switch 13 which in its turn is mechanically coupled to the main circuit-breaker in the direct current circuit in such manner as to be closed when the latter is opened. By thus short-circuiting the winding 12 in itself the currents arising in the damper winding proper are prevented from appreciably influencing the winding 12 and thereby the commutating flux.

It may also be advisable to short-circuit the ordinary commutating winding traversed by the main current when the latter current is broken. An arrangement for this purpose is shown in Figure 10 where the commutating winding is designated by 15, the switch for its short-circuiting by 16 and the main circuit-breaker coupled thereto by 14. The commutating pole may also here be provided with some additional turns from the damper winding which are however not shown in order not to complicate the drawings.

l/Vhile, on several occasions commutating poles have been referred to in the specification, it is not essential that particular pole cores should be present in the commutating zone or that such cores, if present, should immediately traverse the turns or loops embracing the commutating zone. The only essential feature is the position of these loops or turns with respect to the commutating zone.

I claim as my invention:

1. A synchronous converter having a com mutating zone and comprising main poles, commutating poles, and including elements of magnetic material in said commutating zone adjacent at least some of said commutating poles, and a closed damper winding which comprises axial conductors traversing the main poles and peripheral end conductors connecting said axial conductors and extending into the commutating zone and being bent to form turns around at least portions of at least some of said elements.

2. A synchronous converter comprising main poles, commutating poles, and a closed damper winding which comprises axial conductors traversing the main poles, and peripheral end conductors connecting said axial conductors at least some of said end conductors forming at least a portion of a turn around at least a portion of at least some of said commutating poles.

3. A synchronous converter having main poles, commutating poles and commutating zones adjacent said commutating poles, and including elements of magnetic material in said communicating zones adjacentat least some of said commutating poles, and a closed damper winding which comprises axial conductors traversing the main poles, peripheral end conductors connecting said axial conductors and extending into the commutating zones and being bent to form turns around at least portions of at least some of said elements, and axial conductors connecting said end pieces between the main poles and the commutating zones to form a return path for the current.

4:. A synchronous converter having main poles, commutating poles and commutating zones adjacent said commutating poles, and including elements of magnetic material in said commutating zones adjacent at least some of said commutating poles, and a closed damper winding which comprises axial conductors traversing the main poles, peripheral end conductors connecting said axial conductors and extending into the commutating zones and being bent to form turns around at least portions of at least some of said elements, and conducting loops located between the main poles and the commutatin g zones and embracing a portion of the flux therebetween.

5. A synchronous converter having main poles, commutating poles and commutating zones adjacent said commutating poles, and including elements of magnetic material in said commutating zones adjacent at least some of said commutating poles, and a closed damper winding which comprises axial conductors traversing the main poles, peripheral end conductors connecting said axial conductors and extending into the commutating zones and being bent to form turns around at least portions of at least some of said elements, axial conductors connecting said end pieces between the main poles and the commutating zones to form a return path for the current, and conducting loops located between the main poles and the commutating zones and embracing a portion of the flux therebetween.

In testimony whereof I have signed my name to this specification.

LUDVVIG DREYFUS. 

